 /*******************************************************************************
  * Copyright (c) 2000, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.text.undo;

 import java.util.HashMap ;
 import java.util.Map ;

 import org.eclipse.core.runtime.Assert;

 import org.eclipse.jface.text.IDocument;

 /**
  * This document undo manager registry provides access to a document's
  * undo manager. In order to connect a document a document undo manager
  * call <code>connect</code>. After that call has successfully completed
  * undo manager can be obtained via <code>getDocumentUndoManager</code>.
  * The undo manager is created on the first connect and disposed on the last
  * disconnect, i.e. this registry keeps track of how often a undo manager is
  * connected and returns the same undo manager to each client as long as the
  * document is connected.
  * <p>
  * <em>The recoding of changes starts with the first {@link #connect(IDocument)}.</em></p>
  * <p>
  * This class is not intended to be subclassed.
  * </p>
  *
  * @since 3.2
  */
 public final class DocumentUndoManagerRegistry {
     
     private static final class Record {
         public Record(IDocument document) {
             count= 0;
             undoManager= new DocumentUndoManager(document);
         }
         private int count;
         private IDocumentUndoManager undoManager;
     }
     
     private static Map fgFactory= new HashMap ();
     
     private DocumentUndoManagerRegistry() {
         // Do not instantiate
 }

     
     /**
      * Connects the file at the given location to this manager. After that call
      * successfully completed it is guaranteed that each call to <code>getFileBuffer</code>
      * returns the same file buffer until <code>disconnect</code> is called.
      * <p>
      * <em>The recoding of changes starts with the first {@link #connect(IDocument)}.</em></p>
      *
      * @param document the document to be connected
      */
     public static synchronized void connect(IDocument document) {
         Assert.isNotNull(document);
         Record record= (Record)fgFactory.get(document);
         if (record == null) {
             record= new Record(document);
             fgFactory.put(document, record);
         }
         record.count++;
     }

     /**
      * Disconnects the given document from this registry.
      *
      * @param document the document to be disconnected
      */
     public static synchronized void disconnect(IDocument document) {
         Assert.isNotNull(document);
         Record record= (Record)fgFactory.get(document);
         record.count--;
         if (record.count == 0)
             fgFactory.remove(document);
             
     }

     /**
      * Returns the file buffer managed for the given location or <code>null</code>
      * if there is no such file buffer.
      * <p>
      * The provided location is either a full path of a workspace resource or
      * an absolute path in the local file system. The file buffer manager does
      * not resolve the location of workspace resources in the case of linked
      * resources.
      * </p>
      *
      * @param document the document for which to get its undo manager
      * @return the document undo manager or <code>null</code>
      */
     public static synchronized IDocumentUndoManager getDocumentUndoManager(IDocument document) {
         Assert.isNotNull(document);
         Record record= (Record)fgFactory.get(document);
         if (record == null)
             return null;
         return record.undoManager;
     }

 }

